The fabrication of electronic assemblies, such as integrated circuit chips, typically involves inspection of the device at various phases of the fabrication process. Such inspection procedures often utilize vision systems or image processing systems (e.g., systems that capture images, digitize them and use a computer to perform image analysis) to guide the fabrication machine for correct placement and/or alignment of components.
In fabricating such electronic assemblies, wire bonding is typically used to interconnect the integrated circuit chip with a lead frame. Other well-known interconnect processes include, for example, ball-bumping and stud-bumping. As part of these bonding processes a bonding ball is formed at the end of the bonding wire using a well-known electric flame-off (EFO) technique. The size (diameter) of the bonding ball (free air ball) depends on the current and duration of the EFO. As wire bonders are used for packaging finer and finer pitch devices, it would be desirable to measure and control free air ball diameters in an effort to regulate ball size for ultra fine pitch application.
A conventional vision system (shown in FIG. 11) consists of two image devices, a first image device 1104 placed below workpiece plane 1112 and upwardly viewing objects and a second image device 1102 placed above workpiece plane 1112 and downwardly viewing objects. These conventional systems have drawbacks in that in addition to requiring more than one image device, they are unable to easily compensate for variations in the system due to thermal changes, for example.
Further, in conventional systems, bonding ball diameter is typically measured off-line. That is, the bonding process is interrupted so that the ball diameter or the resultant stud (in the case of stud-bumping) can be measured. Changes in the size of the bonding ball are then made to the EFO system, again off-line, to correct for the size of the bonding ball. Thus, the bonding ball size is measured and adjusted via an off-line calibration sequence and programmed into the wire bonder.
These conventional systems have deficiencies, however, in that they have no way of determining the effect of these settings without again going to an off-line measurement. Thus, the ball size determination and control is open loop and requires interrupting the bonding process, negatively impacting device throughput.
Accordingly, it would be desirable to provide a system and method for allowing a wire bonder to periodically measure the ball diameter so that the EFO system may be controlled to produce the desired size ball continuously without the necessity to interrupt the ball bonding process with off-line measurements and adjustments.